fix: hide masked values in log files (#1011)

this commit adds support for the `::add-mask::` command, which was
implemented as a stub before.

it does not cover debug output that appears when you run act in
verbose mode

Co-authored-by: Björn Brauer <bjoern.brauer@new-work.se>
Co-authored-by: Markus Wolf <markus.wolf@new-work.se>

Co-authored-by: Björn Brauer <bjoern.brauer@new-work.se>
Co-authored-by: Markus Wolf <markus.wolf@new-work.se>

pkg/runner/command.go

@@ -55,6 +55,7 @@ func (rc *RunContext) commandHandler(ctx context.Context) common.LineHandler {
 		case "error":
 			logger.Infof("  \U00002757  %s", line)
 		case "add-mask":
+			rc.AddMask(arg)
 			logger.Infof("  \U00002699  %s", "***")
 		case "stop-commands":
 			resumeCommand = arg